Arrangement and process for communication between an ignition module and control unit in a combustion engine&#39;s ignition system

ABSTRACT

An arrangement and a process for communication between an ignition module (ICM) mounted on an engine and a control unit (ECM). The ignition module includes detection circuits and signal processing stages in order to determine at least one combustion related parameter from detected ionization currents in the combustion chamber (22). The control unit (ECM) communicates with the ignition module via at least one bi-directional communication wire (K CQ  or K KI ). Via the communication wire the control unit activates the detection in the ignition module, and the ignition module sends a signal corresponding to the magnitude of the detected parameter to the control unit on the same communication wire. Activation and transfer of parameter data is conducted sequentially over the communication wire.

BACKGROUND OF THE INVENTION

The present invention refers to an arrangement and process forcommunication between an ignition module mounted on an engine and thecontrol unit in a combustion engine's ignition system.

STATE OF THE ART

In ignition systems with detection of the degree of ionisation in thecombustion chamber, preferably via the spark plug gap, a number ofcombustion related parameters can be detected via the ionisationcurrent. In the systems which are used in motor vehicles, e.g. in theSAAB 2.3 liter four-cylinder petrol engines, an amplified analoguesignal in relation to the degree of ionisation is sent from an ignitionmodule mounted on the engine, or ignition cassette, up to the ignitionsystem's control unit. The knock intensity is then detected in thecontrol unit via the filtering out of a representative frequency contentin relation to the knock in the amplified analogue ionisation signal.

One risk with these systems is that the analogue information issensitive to interference, and that a great deal of the informationwhich exists in the ionisation signal can be lost during theamplification or signal processing before the signal is sent to thecontrol unit.

One preference is therefore that the determination of the differentcombustion related parameters should be conducted as close to the engineas possible, i.e. in the ignition module/ignition cassette. Such apartitioning of the system, however, sets requirements on the transferof information and the activation of the different detection processes,which detection processes must be activated at different times and inrelation to the engine's actual load and speed. A natural arrangementwould therefore be to introduce an individual signal wire between thecontrol unit and ignition module for each of the different parametervalues which are to be transferred, and individual signal wires foractivation/triggering of the detection functions.

The invention has the objective of reducing the number of wires betweenan ignition module mounted on the engine and its control unit, where theignition module can locally determine at least one of the parametersrelated to combustion, based on the detected degree of ionisation in thecombustion chamber. By reducing the number of wires the ignition systemcan be made more reliable with the minimisation of the number of contactpoints, also achieving a reduction of the cabling costs. This is veryimportant during the installation of electronics and additional cabling,above all in the exposed environment in an engine compartment of a motorvehicle.

A further objective is to enable a standardisation of the ignitionmodule, where the ignition module contains all the means for determiningat least one signal related to the combustion quality and one signalrelated to the knock intensity, but where all corrections andinitiations of the detection in accordance with predetermined algorithmsare determined in the control unit. Each ignition system can hereby beeasily adjusted to different types of engines by modification in thecontrol unit, but where the ignition module consists of a standardisedunit in the ignition system. The combustion process can differ betweendifferent combustion engines, and also the requirements for combustionquality and permissible knock level can differ between different typesof applications. This makes it necessary to adjust the detectionstrategies to different types of engines.

Yet another objective with a favourable design is that at least twosignal processing stages can be activated at least partially in paralleland transfer at least partially in parallel different combustion relatedparameters on the respective communication wire.

SUMMARY

An arrangement and process in accordance with the present invention foraccomplishing the foregoing and other objects includes providing a cablefor communication between the control unit and the ignition module, thecable containing at least one individual trigger wire for each primaryswitch in the ignition module and one first bi-directional communicationwire for each ignition module, the first bi-directional communicationwire being used to activate a signal processing unit and to transferinformation concerning the first combustion related parameter from theignition module to the control unit. The information is obtained via adetection circuit and a signal processing unit as a function of thecombustion process, the activation and transfer of information via thecommunication wire being sequential.

By means of the arrangement and process in accordance with the inventionit is possible for both activation of an ion current analysis, andtransfer of a combustion related parameter determined from the ioncurrent analysis, using only one bi-directional communications wire.This reduces the number of wires and contact points between the controlunit and ignition module, which increases reliability and reduces thecost of the ignition system. Each wire and contact point constitute apotential fault source.

Other special features and advantages of the invention are indicated inthe subsequent description of a design example with reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a combustion engine with an ignition module mounted on theengine and a control unit arranged at a distance from the engine.

FIG. 2 shows an ignition module for a four-cylinder Otto-engine.

FIG. 3 shows matching circuits, interface, for bi-directionalcommunication in accordance with the invention.

FIG. 4 shows a signal status diagram for trigger signal, combustionquality signal, and knock signal in relation to the position of theengine (crankshaft degrees, CD).

PREFERRED EMBODIMENT(S)

The invention is applied on combustion engines 20 of the Otto type, seeFIG. 1, equipped with at least one ignition module mounted on theengine, ICM (Ignition Control Module), and a control unit, ECM (EngineControl Module). The control unit is placed in the motor vehicle,preferably mounted at a distance from the engine, either on the cowlwall in the engine compartment or protected inside the vehicle's coupe.The combustion engine is equipped with a number of sensors, for example:

One load sensor 12, arranged in the induction pipe 21 (alternatively athrottle position sensor).

One engine temperature sensor 13.

One engine position sensor 14, arranged by the engine's flywheel 25,where a number of cogs on the flywheel in an inherently known mannergenerate pulses from the sensor 14. A number of cogs are shapeddifferently, whereby the engine position, i.e. the rotational positionsof the crankshaft 26 and thereby also the position of the pistons 23 inthe engine's combustion chamber 22 can be determined.

The sensors 12-14 are connected to the control unit ECM, whereby notonly ignition but also the fuel supply can be regulated depending on thedetected engine load, engine temperature, position and speed of theengine. The control unit ECM controls, depending on the detected engineparameters, via trigger signal wires T1-T4 when the ignition module ICMshall generate an ignition spark. The trigger signal wires shown in thedesign example are four individual trigger signal wires for eachignition coil. The ignition coils are preferably directly connected onrespective ignition plugs (see FIG. 2) in a four-cylinder engine. Theignition module is also supplied with current via a two-wire P,Gconnected to both poles of the power source. The control unit ECM alsoreceives its current via a power source, preferably at battery 10. Inaccordance with the invention the cabling L between the control unit ECMand the ignition module ICM also contains at least one bi-directionalcommunications wire, K_(KI) or K_(CQ).

FIG. 2 shows the structure of the ignition module, ICM, for afour-cylinder Otto-engine. In the design example shown a detectioncircuit 39a is used for two ignition circuits 32a-33a-34a-35a, and32b-33b-34b-35b. These ignition circuits generate the ignition spark inthe spark plugs 24a and 24b, arranged in two different cylinders wherethe pistons have a phase displacement of 180 crankshaft degrees. Theunit 60a, with two ignition circuits and one common detection circuit39a, is identical with the other unit 60b, which generates the ignitionspark in the spark plugs 24c and 24d.

The trigger signals T1-T4 go via a processor CPU to circuit breakers orprimary switches 35a and 35b in the unit 60a and circuit breakers orprimary switches 35c and 35d in the unit 60b, via the signal wirest1-t4. In each cylinder 22 at least one spark plug 24a-24d is arranged.The function is described in more detail with reference to thegeneration of an ignition spark in the spark plug 24a. The ignitionvoltage is generated in an ignition coil 32a with primary winding 33aand secondary winding 34a. The primary winding 33a is in one endconnected to a voltage source, P, and an electrically controlledcircuit-breaker 35a is arranged in its earth connection. In that theprocessor on the trigger outlet t1 switches the circuit-breaker 35a to aconductive state, a current begins to flow through the primary winding33a, and when the current is interupted a step-up transformed ignitionvoltage is induced in the normal manner in the ignition coil's 32asecondary winding 34a and an ignition spark is generated in the sparkplug gap. When the current is to be turned on and when the current is tobe switched off by the circuit-breaker 35a, so-called dwell-timeregulation, is controlled in accordance with the pre-stored ignitionangle map in the control unit's memory depending on the engineparameters in question. The dwell-time regulation ensures that thenecessary primary current has time to develop and that the ignitionspark is generated at the ignition point which is required for the loadcase in question.

One end of the secondary is connected to the spark plug 24a and in itsother earth connected end there is a detection circuit 39a which detectsthe degree of ionisation in the combustion chamber. The detectioncircuit includes a voltage accumulator, here in the form of a chargeablecondenser 40, which applies a bias voltage over the spark plug gap withan essentially constant measuring voltage. The condenser corresponds toan equivalent solution to the design example shown in EP,C,188180, wherethe voltage accumulator is an enhanced/step-up transformed voltage fromthe charging circuit in a capacitive ignition system. In the designexample shown in the figure the condenser 40 is charged up to a voltagelevel given by the Zener diode's 41 breakdown voltage when the ignitionvoltage pulse is induced in the secondary winding 34a. This breakdownvoltage can lie somewhere between 80-400 volts. The Zener diode breaksdown when sufficient current has been generated for the condenser to becharged up to a voltage level corresponding to the Zener diode'sbreakdown voltage. An inverse protective diode 43 is arranged inparallel with the measuring resistance 43 which correspondingly providesprotection from voltages with inverse polarity.

Over the measuring resistance 42 the current which goes in circuit24a-34-40/40-42-earth can then be detected, which current depends on theconductivity of the gases in the combustion chamber, and whichconductivity is proportional to the degree of ionisation in thecombustion chamber.

In that the measuring resistance 42 is connected closest to earth, onlyone connection is required in the measuring point 45 to a signalprocessing unit 44, which signal processing unit measures the voltageover the resistance 42 and in the measuring point 45 in relation toearth. By analysing the current through, or alternatively the voltageover the measuring resistance, it is possible to detect knocking andpre-ignition, and as described in U.S. Pat. No. 4,535,740 it should bepossible to detect the actual mixing ratio of air and fuel duringcertain operating cases by measuring how long the ionisation currentexceeds a certain level.

The signal processing unit 44 shown produces a signal corresponding tothe combustion quality, CQ/Combustion Quality, and a signalcorresponding to the knock intensity, KI/Knock Intensity, in twoparallel signal processing stages 52a,53a and 52b,53b. A representativevalue in relation to a knocking condition is obtained in a signalprocessing stage by extracting out the typical frequency content for aknocking condition. This is done in a band-pass filter/BPF, 52b, wherethe band-pass filter's centre frequency is set to the knock frequency,which knock frequency is dictated by the engine geometry. For aconventional 2 liter four-cylinder Otto-engine the centre frequency cantypically lie at some 5 kHertz. Thereafter the band-pass filtered signalis rectified and integrated in an integrator 53b. The signal, KI_(DATA),which is obtained from the integrator 53b will therefore be proportionalto the knock intensity.

A representative value for the combustion quality is obtained in asimilar manner in a second signal processing stage, by means of blockingout high frequency components in the ion current signal. This is done ina low-pass filter 52a. Thereafter the low-pass signal is integrated inan integrator 53a. The signal, CQ_(DATA), obtained from the integrator53a will therefore be proportional to the combustion intensity, whichcan be used as a measure of the combustion quality.

The measuring window signals CQ_(w) and KI_(w) are sent to therespective filters 52a/52b from the processor when the filtering inrespective filters 52b and 52a is to be initiated. The measuring windowsignals activate the filter in the measuring window, which measuringwindow is controlled by the control unit, ECM, in a manner which isdescribed in more detail in connection with FIG. 4.

Since the signal processing unit 44 contains relatively expensivecomponents a change-over switch 51 is used, which depending on a signalon a wire SW from a logic circuit switches between the detection circuit39a in the unit 60a and a corresponding detection circuit 39b in theunit 60b. The change-over switch 51 is schematically reproduced in thefigure as a relay controlled circuit-breaker, which with conventionalIC-circuits can be realised with a MUX(multiplex)-circuit, controlled bythe processor CPU. This is conducted depending on the trigger signalsfrom the control unit ECM. When the ignition sequence has beendetermined the change-over switch 51 begins to switch so that either thesignal on wire J1 or J2 is connected to the signal processing unit 44depending on in which cycle combustion takes place. With the ignitionsequence 1-3-4-2 the change-over switch first stands in the positionshown in the figure when cylinder 1 fires, after which the change-overswitch changes during the time cylinder 3 and 4 fire, in order to returnto the position shown when cylinder 2 fires. This assumes that sparkplug 24a is in cylinder 1, 24b in cylinder 2, 24c in cylinder 3, and 24din cylinder 2.

If cylinder identification, i.e. firing order determination, takes placeduring start of the engine with ion current detection, the firing isgenerally generated in both cylinders where the pistons simultaneouslyreach top dead centre, when one cylinder is at the end of the exhaustphase and the other cylinder is in the end phase of compression of thefuel-air mixture. The ionisation signal becomes considerably higher fromthe cylinder where combustion occurs, which is used to determine thefiring order. In order to ensure that the firing order is determinedcorrectly some 10 confirmative determinations of the firing order arerequired. If a change-over switch 51 in accordance with FIG. 2 is usedthe change-over switch must stand in a fixed position until the firingorder has been determined. This implies that a number of combustions inthe engine must be activated before the firing order is unequivocallydetermined, since only combustions from two of the engine's fourcylinders provide the basis for the determination of the firing order.Once the firing order has been determined a spark is only generated inthe cylinder where the piston reaches the end of the compression stroke,and the change-over switch 51 begins to adjust to the cylinders whichare in firing position.

The processor contains an A/D converter, where the analogue signalsKI_(DATA) and CQ_(DATA) are converted to digital signals, preferablypulse width modulated (PWM-modulation). In accordance with the inventionthe ignition module's processor CPU sends the signal KI_(DATA)corresponding to the knock intensity via a adaptation matching circuit50b, by putting out a digital signal on the wire P_(OUT/KI) having apulse width which is proportional to the analogue integrated value fromthe integrator 53b. In the same manner the ignition module's processorCPU sends the analogue signal CQ_(DATA) corresponding to the combustionquality via a an adaptation or matching circuit 50a by putting out adigital signal on the wire P_(OUT/CQ) having a pulse width which isproportional to the integrated value from the integrator 53a.

The adaptation or matching circuits 50a/50b and 50c/50d which areincluded in the ignition module and control modules respectively areindicated in FIG. 3, and this type of matching unit is located at eachend of the communication wires K_(CQ) and K_(KI), i.e. matching units50c/50d in the control unit and matching units 50a/50b in the ignitionmodule. The matching circuit is of the active-low type, where the signalis present when the signal level on the K_(CQ) /K_(KI) wire is low.K_(CQ) /K_(KI) is connected to a supply voltage/VCC via a resistance R2.With 5 volts logic the VCC lies at a voltage level of 5 volts. If, forexample, the ignition module in its end activates its output P_(OUT)then SI is reset to a conductive status, whereby K_(CQ) /K_(KI) isconnected to earth and assumes a low/active signal. The low status onK_(CQ) /K_(KI) is detected by the control unit in the other end of thecommunication wire K_(CQ) /K_(KI) via its signal input P_(IN).

An inverter INV inverts the active low signal on K_(CQ) /K_(KI) to anactive high signal for the ECM and the CPU. The function of the matchingunits is described in more detail with reference to the signal statusdiagram shown in FIG. 4. At the point in time A the control unit ECMsends out a signal on the wire T1 which via the processor switches theprimary switch 35a for cylinder 1 into a conductive status with a signalon the wire t1. This signal also initiates the processor in the ignitionmodule to send up the value in the integrators 53a and 53b obtained fromthe previous combustion, which in FIG. 4 correspond to the pulse widthCQ_(cy12) and KI_(cy12), obtained from the combustion in cylinder 2. Theprevious combustion has occurred in cylinder 2 in a four-cylinder enginewith the firing order 1-3-4-2. The pulse widths on CQ_(cy12) andKI_(cy12) are preferably proportional to CQ_(DATA) and KI_(DATA)obtained from the two signal processing stages 52a,53a and 52b,53b.

At the point in time B the trigger signal on the wire T1 goes low whichswitches the primary switch into a non conductive status, whereby thespark is generated, which normally occurs a few crankshaft degrees/CDprior to the top dead centre. The top dead centre for cylinder 1corresponds to 0 CD on the x-axis in FIG. 4. When combustion starts thedetection of the combustion quality is initiated, which takes place atthe point in time C controlled by the control unit by means ofactivating the measuring window, with the signal CQ_(w-cy11). Thecontrol unit ECM activates its output P_(OUT) which activates S1 to aconductive status, whereby K_(CQ) /K_(KI) is connected to earth andassumes a low/active signal. The low signal in the communication wireK_(CQ) is detected by the ignition module's processor CPU on the inputP_(IN/CQ), whereby the processor activates the filter 52a via the signalwire CQ_(w).

The pressure oscillations typical for a knocking condition always occurat a later stage of the combustion. The control of the knock measuringwindow is conducted in a similar manner. When knocking can occur theknock detection is initiated, which takes place at the point in time Dcontrolled by the control unit by activating the measuring window, withthe signal KI_(w-cy11). The control unit ECM activates its outputP_(OUT), which activates S1 to a conductive status, whereby thecommunication wire K_(KI) is connected to earth and assumes a low/activesignal.

The low signal on the communication wire K_(KI) is detected by theignition module's processor CPU on the input P_(IN/KI), whereby theprocessor activates the filter 52b via the signal wire KI_(w). At thepoint in time E the control unit ECM closes the measuring window forknock and combustion quality in that the respective output P_(OUT) isdeactivated, whereby K_(KI) and K_(CQ) assume a high non active signal.

The invention can be modified in a number of ways within the frameworkof attached claims. The matching circuits 50a/50b and 50c/50d in theignition module and control unit can, instead of being of the active-lowtype, be of the active-high type. The parameters determined from theionisation signal can be more than two or refer to other combinations oftwo at least partially parallel measurements. For example, a thirdsignal, which depends on how long the ionisation signal has exceeded apredetermined or an engine parameter related signal level, can replaceone of the given parameters CQ or KI in the design example, oralternatively supplement these.

The combustion engine can also have more or less than four cylinders,for example, 2, 6, 8 or 12 cylinders. In certain engines it is alsopossible to use more than one ignition module, for example in V-engineswhere an ignition module is arranged on respective cylinder banks.

The signal processing unit 44 can also be activated such that theinitiation signal CQ_(w) and KI_(w) directly starts and concludes theintegration in stages 53a and 53b. The resetting of the integrators canbe handled by the CPU, for example dependent of CQ_(DATA) and KI_(DATA)being collected by the processor CPU. The invention can also beimplemented in ignition systems where the control unit is arranged onthe engine, but where a cable connects the control unit mounted on theengine with the ignition modules. The invention can also be used incapacitive ignition systems, where the primary switch 35a/35b dischargesinstead from a condenser via the primary winding.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claimed is:
 1. Arrangement for communication in an ignitionsystem between at least one ignition module mounted on a combustionengine and a control unit physically separated from the ignition moduleand arranged at a distance from the ignition module, wherein theignition module includes at least one ignition coil with a primarywinding and a secondary winding, at least one detection circuit fordetecting an ionization current in a spark plug gap connected to thesecondary winding, and a signal processing unit connectable to thedetection unit, the signal processing unit containing means to determineat least one combustion parameter from the detected ionization current,the ignition module including a primary switch connected to the ignitioncoil's primary winding by means of which primary switch the control unitcontrols the current through the primary winding and thereby induces anignition voltage in the spark plug gap, the arrangement beingcharacterized in that the control unit communicates with the ignitionmodule via a cable containing at least,one individual trigger wire foreach primary switch in the ignition module, and one first bi-directionalcommunication wire for each ignition module where the firstbi-directional communication wire is used to activate the signalprocessing unit from the control unit, and to transfer informationconcerning a first combustion related parameter from the ignition moduleto the control unit, which information is obtained via the detectioncircuit and the signal processing unit from the combustion process, andwhere activation and the transfer of information via the communicationwire is sequential.
 2. An arrangement in accordance with claim 1,wherein the cable further includes a second bi-direction wire for eachignition module, the first and second bi-directional communication wiresbeing used to partially parallel activate two signal processing stagesin the signal processing unit connected to the detection circuit, andtransfer at least partially parallel information concerning a first andsecond combustion related parameter from the ignition module to thecontrol unit, which information is obtained in the respective signalprocessing stages from the combustion process, and where activation andthe transfer of information via a respective one of first and secondcommunication wires is sequential.
 3. An arrangement in accordance withclaim 1 or 2, in which each of the first and second communication wireshas a first end connected to the control unit via a first matchingcircuit and its other end connected to the ignition module via a secondmatching circuit.
 4. An arrangement in accordance with claim 3, whereineach matching circuit contains a drive connection to the control unitand ignition module and a signal input to the control unit and ignitionmodule, the drive connection on activation from the control unit andignition module, respectively, via switch means, switching the signalstatus on the respective communication wire from a first signal level toa second signal level, and the signal input detecting the actual signallevel on the respective communication wire.
 5. An arrangement inaccordance with claim 4, wherein the control unit via its driveconnection for the respective communication wire activates a signalprocessing state in the signal processing unit.
 6. Process forcommunication in an ignition system between at least one ignition modulemounted on a combustion engine and one control unit physically separatedfrom the ignition module and arranged at a distance from the ignitionmodule, the ignition module including at least one ignition coil with aprimary winding and a secondary winding, at least one detection circuitfor detecting an ionization current in a spark plug gap connected to thesecondary winding, and a signal processing unit connectable to thedetection unit, the signal processing unit containing means determiningat least one combustion parameter from the detected ionization currentand the ignition module including a primary switch connected to theignition coil's primary winding by means of which primary switch thecontrol unit controls the current through the primary winding andthereby induces an ignition spark in the spark plug gap, the processcomprising the steps of:communicating between the control unit and theignition module via at least one for each ignition module individualfirst bi-directional communication wires, the first bi-directioncommunication wire being used to activate the signal processing unitfrom the control unit for detection of a first combustion relatedparameter, and to transfer information concerning the first combustionrelated parameter from the ignition module to the control unit, theactivation and the transfer of information being sequential andsynchronous with the inducement of the ignition spark initiated by thecontrol unit.
 7. Process for communication in an ignition system betweenat least one ignition module mounted on a combustion engine and onecontrol unit physically separated from the ignition module and arrangedat a distance from the ignition module, the ignition module including atleast one ignition coil with a primary winding and a secondary winding,at least one detection circuit for detecting an ionization current in aspark plug gap connected to the secondary winding, and a signalprocessing unit connectable to the detection unit, the signal processingunit containing means determining at least one combustion parameter fromthe detected ionization current and the ignition module including aprimary switch connected to the ignition coil's primary winding by meansof which primary switch the control unit controls the current throughthe primary winding and thereby induces an ignition spark in the sparkplug gap, the process comprising the steps of:communicating between thecontrol unit and the ignition module via at least one for each ignitionmodule individual first bi-directional communication wires, the firstbi-direction communication wire being used to activate the signalprocessing unit from the control unit for detection of a firstcombustion related parameter, and to transfer information concerning thefirst combustion related parameter from the ignition module to thecontrol unit, the activation and the transfer of information beingsequential and synchronous with the inducement of the ignition sparkinitiated by the control unit and the bi-directional communication onthe wire being conducted in digital form, the start of detection beinginitiated by the transfer from a first digital signal level to a seconddigital signal level, and the duration of the detection being directlyproportional to the pulse width of the digital signal at the seconddigital signal level, whereby the detection is terminated by thetransfer from the second digital signal level to the first digitalsignal level, and where information concerning the first combustionrelated parameter is transferred at a different time than the activationof the detection by means of a pulse having a pulse width which isproportional to the first combustion parameter's magnitude.
 8. A processin accordance with claim 7, wherein the transfer of the informationconcerning the magnitude of the first combustion related parameter issent essentially synchronously with switching of the primary switch to aconductive state by the control unit, and the detection starts after theprimary switch has been switched to a non-conductive state which inducesan ignition spark in the spark plug gap whereby combustion is initiated.